Vertebral compression fractures, as illustrated in FIG. 1, represent a generally common spinal injury and may result in prolonged disability. These fractures involve collapsing of one or more vertebral bodies 12 in the spine 10. Compression fractures of the spine usually occur in the lower vertebrae of the thoracic spine or the upper vertebra of the lumbar spine. They generally involve fracture of the anterior portion 18 of the affected vertebra 12 (as opposed to the posterior side 16). Spinal compression fractures can result in deformation of the normal alignment or curvature, e.g., lordosis, of vertebral bodies in the affected area of the spine. Spinal compression fractures and/or related spinal deformities can result, for example, from metastatic diseases of the spine, from trauma or can be associated with osteoporosis. Until recently, doctors were limited in how they could treat such compression fractures and related deformities. Pain medications, bed rest, bracing or invasive spinal surgery were the only options available.
More recently, minimally invasive surgical procedures for treating vertebral compression fractures have been developed. These procedures generally involve the insertion of a rigid cannula, needle or trocar inserted into the interior of a collapsed or otherwise damaged vertebral body. The cannula may include a lumen or central passage through which another tool, implant or filler material may be passed in order to reposition and/or augment the vertebral body. A common surgical approach to the interior of a vertebral body is from the posterior side, e.g., through one or both pedicles as shown in FIG. 2.
The most basic of these procedures is vertebroplasty, which literally means fixing the vertebral body, and may be done without first repositioning the bone. Briefly, a cannula or special bone needle is passed slowly through the soft tissues of the back. Image guided x-ray, along with a small amount of x-ray dye, allows the position of the needle to be seen at all times. A small amount of polymethylmethacrylate (PMMA) or other orthopedic bone cement is pushed through the needle into the vertebral body. PMMA is a medical grade substance that has been used for many years in a variety of orthopedic procedures. Generally, the cement is mixed with an antibiotic to reduce the risk of infection, and a powder containing barium, tantalum, or iodine solution which allows it to be seen on the X-ray.
Vertebroplasty can be effective in the reduction or elimination of fracture pain, prevention of further collapse, and a return to mobility in patients. However, this procedure may not reposition the fractured bone and therefore may not address the problem of spinal deformity due to the fracture. It generally is not performed except in situations where the kyphosis between adjacent vertebral bodies in the effected area is less than 10 percent. Moreover, this procedure requires high-pressure cement injection using low-viscosity cement, and may lead to cement leaks in 30-80% of procedures, according to recent studies. In most cases, the cement leakage does no harm. In rare cases, however, polymethymethacrylate or other cement leaks into the spinal canal or the perivertebral venous system and causes pulmonary embolism, resulting in death of the patient.
A number of more advanced treatments for vertebral compression fractures are known, and generally involve two phases: (1) reposition, or restoration of the original height of the vertebral body and consequent lordotic correction of the spinal curvature; and (2) augmentation, or addition of material to support or strengthen the fractured bone. As with vertebroplasty, such procedures generally involve use of a cannula, catheter, needle, trocar or other introducer to provide access to the interior of an effected vertebral body.
For example, one such treatment, balloon kyphoplasty (Kyphon, Inc.), is illustrated in FIGS. 3A-D. A catheter having an expandable balloon tip is inserted through a cannula, sheath or other introducer into a central portion of a fractured vertebral body comprising relatively soft cancellous bone surrounded by fractured cortical bone (FIG. 3A). Kyphoplasty then achieves the reconstruction of the lordosis, or normal curvature, by inflating the balloon, which expands within the vertebral body restoring it to its original height (FIG. 3B). The balloon is removed, leaving a void within the vertebral body, and PMMA or other filler material such as, for example, bone cement, is then injected through the cannula into the void (FIG. 3C) as described above with respect to vertebroplasty. The cannula is removed and the cement cures to augment, fill or fix the bone (FIG. 3D).
Disadvantages of this procedure include the high cost, the loss in height of the vertebral body after the removal of the balloon catheter, the high pressures required to impart sufficient force to separate or maintain the separation of the vertebral endplates, and the possible perforation of the vertebral endplates during the procedure. As with vertebroplasty, perhaps the most feared, albeit remote, complications related to kyphoplasty are related to leakage of bone cement. For example, a neurologic deficit may occur through leakage of bone cement into the spinal canal. Such a cement leak may occur through the low resistance veins of the vertebral body or through a crack in the bone which has not been appreciated previously. Other complications include; additional adjacent level vertebral fractures, infection and cement embolization. Cement embolization occurs by a similar mechanism to a cement leak. The cement may be forced into the low resistance venous system and travel to the lungs or brain resulting in a pulmonary embolism or stroke. Additional details regarding balloon kyphoplasty may be found, for example, in U.S. Pat. Nos. 6,423,083, 6,248,110, and 6,235,043 to Riley et al., each of which is incorporated by reference herein in its entirety.
Another procedure for treating vertebral compression fractures is the Optimesh system (Spineology, Inc., Stillwater, Minn.), which provides minimally invasive delivery of a cement or allograft or autograft bone using an expandable mesh bag, or containment device, within the involved vertebral body. The bag or graft remains inside the vertebral body after its inflation, which prevents an intraoperative loss of reposition, such as can occur during a kyphoplasty procedure when the balloon is withdrawn. The optimesh system may also prevent leakage of the cement or bone material which is captured or contained by the bag. One drawback of this system, however, is that the mesh implant is not well integrated in the vertebral body. This can lead to relative motion between the implant and vertebral body, and consequently to a postoperative loss of reposition. The system is also complex and relatively expensive. Additional details regarding this procedure may be found, for example, in published U.S. Patent Publication No. 20040073308, which is incorporated by reference herein in its entirety.
Still another procedure used in the treatment of vertebral compression fractures is an inflatable polymer augmentation mass known as a SKy Bone Expander. This device can be expanded up to a pre-designed size and Cubic or Trapezoid configuration in a controlled manner. Like the Kyphon balloon, once optimal vertebra height and void are achieved, the SKy Bone Expander is removed and PMMA cement or other filler is injected into the void. This procedure therefore entails many of the same drawbacks and deficiencies described above with respect to kyphoplasty.
Thus, a common drawback of most known systems and procedures for repositioning and augmenting damaged vertebrae is that they involve the use of relatively complex apparatus introduced through rigid introducers. The rigid introducers can damage the vertebral pedicles and/or surrounding tissues during insertion and/or manipulation of the augmentation apparatus. Accordingly, there remains a need in the art to provide safe and effective apparatus and methods for minimally invasive repositioning of and osteopathic augmentation of vertebral bodies to restore lordosis of the spine.
Regardless of the type of implant or augmentation method used, however, any such treatment of a collapsed or otherwise fractured vertebral body generally must be performed within about six weeks of the injury. Otherwise, the fractured bones may tend to heal in their collapsed state, making it difficult or impossible to reposition the affected vertebral bodies and/or restore lordosis without first disrupting, or breaking up, the improperly healed fracture. Moreover, because of the generally close proximity of nerves, blood vessels and other sensitive soft tissues to the spine, any method for disrupting the affected area of a collapsed vertebral body should be minimally invasive and controlled to avoid damaging such surrounding tissues. Accordingly, there remains a need in the art for suitable tools or methods to safely and effectively disrupt such improperly healed bones in a minimally invasive way.